Handing off active connections

Abstract

A connection is established between an access terminal and a first radio network controller through a first radio node. The first radio node is controllable primarily by the first radio network controller. The connection is maintained with the first radio network controller as the access terminal moves from a coverage area of the first radio node toward a coverage area of a second radio node. The second radio node is controllable primarily by a second radio network controller and controllable subordinately by the first radio network controller. A connection is also established through the second radio node. Upon a fulfillment of a predetermined criterion, the connection is transferred from the first radio network controller to the second radio network controller.

What is claimed is: 
     
       1. A method performed in a radio access network, the method comprising:
 establishing a session between an access terminal and a first radio network controller through a first radio node, the first radio node being controllable primarily by the first radio network controller, 
 maintaining the session with the first radio network controller as the access terminal moves from a coverage area of the first radio node toward a coverage area of a second radio node, the second radio node being controllable primarily by a second radio network controller and controllable subordinately by the first radio network controller, 
 establishing a route for the session established with the first radio network controller through the second radio node, and 
 responsive to determining that an active set of the access terminal contains only radio nodes which are subordinately controlled by the first radio network controller, initiating an active handoff from the first radio network controller of a first subnet to the second radio network controller of a second subnet including transferring the session from the first radio network controller to the second radio network controller without dropping an active call associated with the session, 
 wherein the first and second radio network controllers are located in different subnets of the radio access network. 
 
     
     
       2. The method of  claim 1  in which the the determination that the active set of the access terminal contains only radio nodes which are subordinately controllable by the first radio network controller is fulfilled when the first radio node is dropped from the active set of the access terminal. 
     
     
       3. The method of  claim 2  in which the first radio node is dropped from the active set of the access terminal when a strength of a signal of the first radio node falls below a minimum threshold. 
     
     
       4. The method of  claim 1  in which the determination that the active set of the access terminal contains only radio nodes which are subordinately controllable by the first radio network controller is fulfilled when a strength of a signal of the first radio node falls below a minimum threshold. 
     
     
       5. The method of  claim 1  in which the connection uses the Ev-DO, CDMA2000, W-CDMA, HSUPA, HSDPA, HSPA, or LTE telecommunications standard. 
     
     
       6. The method of  claim 1  in which the session uses voice over IP (VoIP) protocol. 
     
     
       7. The method of  claim 1  in which the first radio node is also controlled by a third radio network controller. 
     
     
       8. The method of  claim 1  in which the second radio network controller continues to control the session until a second predetermined criterion is fulfilled. 
     
     
       9. The method of  claim 8  in which the session is transferred back to the first radio network controller from the second radio network controller after the second predetermined criterion is fulfilled, the second predetermined criterion being fulfilled when the active set of the access terminal contains only radio nodes that are both controlled subordinately by the second radio network controller and controlled primarily by the first radio network controller. 
     
     
       10. The method of  claim 1  in which the second radio node sends an address of the second radio network controller to the first radio network controller. 
     
     
       11. An apparatus comprising:
 a first radio network controller to: 
 establish a session with an access terminal through a first radio node, the first radio node being controllable primarily by the first radio network controller, 
 maintain the session as the access terminal moves from the coverage area of the first radio node toward a coverage area of a second radio node, the second radio node being controllable primarily by a second radio network controller and controllable subordinately by the first radio network controller, 
 establish a route for the session established with the first radio network controller through the second radio node, and 
 responsive to determining that an active set of the access terminal contains only radio nodes which are subordinately controlled by the first radio network controller, initiate an active handoff from the first radio network controller of a first subnet to the second radio network controller of a second subnet including transferring the session from the first radio network controller to the second radio network controller without dropping an active call associated with the session, 
 wherein the first and second radio network controllers are located in different subnets of a radio access network. 
 
     
     
       12. A computer program stored on a non-transitory machine-readable storage medium, comprising instructions to cause a radio network controller to:
 establish a session to an access terminal through a first radio node, the first radio node being controllable primarily by the first radio network controller, 
 maintain the session as the access terminal moves from the coverage area of the first radio node toward the coverage area of a second radio node, the second radio node being controllable primarily by a second radio network controller and controllable subordinately by the first radio network controller, 
 establish a route for the session established with the first radio network controller through the second radio node, and 
 responsive to determining that an active set of the access terminal contains only radio nodes which are subordinately controlled by the first radio network controller, initiating an active handoff from the first radio network controller of a first subnet to the second radio network controller of a second subnet including transferring the session from the first radio network controller to the second radio network controller without dropping an active call associated with the session, 
 wherein the first and second radio network controllers are located in different subnets of a radio access network. 
 
     
     
       13. A system comprising:
 a first radio network controller, a second radio network controller, a first radio node, and a second radio node, the first and second radio network controllers being located in different subnets of a radio access network, which is: 
 the first radio network controller is configured to establish a session to an access terminal through the first radio node, the first radio node being controlled primarily by the first radio network controller, 
 the first radio network controller is configured to maintain the session as the access terminal moves from the coverage area of the first radio node toward the coverage area of the second radio node, the second radio node being controllable primarily by the second radio network controller and controllable subordinately by the first radio network controller, 
 the first radio network controller is configured to re-route the session established with the first radio network controller through the second radio node, 
 the first radio node controller is configured to, responsive to determining that an active set of the access terminal contains only radio nodes which are subordinately controlled by the first radio network controller, initiate an active handoff from the first radio network controller of a first subnet to the second radio network controller of a second subnet including transferring the session from the first radio network controller to the second radio network controller without dropping an active call associated with the session; and 
 the second radio network controller is configured to assume control of the session upon the fulfillment of a first predetermined criterion. 
 
     
     
       14. The system of  claim 13  in which the first radio node is also controlled by a third radio network controller.